Electron discharge tube having a disk-shaped cathode



Se t. 2, 1952 c. P. KLCPPING 2,609,518

ELECTRON DISCHARGE TUBE HAVING A DISK-SHAPED CATHODE Filed Oct. 20, 1948AGf/l/T Patented Sept. 2, 1952 y ELECTRON DISCHARGE TUBE HAVINGDISK-SHAPED CATHODE i Carel Peter Kltippi'ng, Eindhoven, Netherlands,assignor to Hartford National Bank and Trust Company, Hartford, 001111,,as trustee Application October 20, 1948, Serial No. 55,445 In theNetherlands November 15, 1947 The invention relates to an electricdischarge tube comprising so-called disc-shaped and usually flatelectrodesand to a method of manufacturing such a tube, moreparticularly of correctly spacingthe cathode away fromthe next-followingelectrode. 4

With disc-shaped electrodes correctly spacing the cathode, particularlywhen the spacing must be minute, has a limitation in that frequently thesaid adjustment cannot be carried out until the electrodes have beensealed in the tube. Correct adjustment is, consequently, dependent onthe sealing-in operation and is affected by the deformations of the sealduring cooling. It has therefore already been suggested to press theelectrodes of a diode closely together and during the operation, byheating definite electrode parts, to utilize the expansion of theseparts for spacing apart the active electrode surfaces. Firstly there istherefore the disadvantage that the relative electrode spacing dependswholly on the operating conditions and this measure can be adopted onlywith systems in which the electrodes are constructed so as to be veryrigid. However, as a rule, such construction is not possible andparticularly with tubes comprising grid-shaped electrodes this methodcannot be carried out in practice, since even a low pressure wouldresult in resilient deformations of the grid so that on spacing theelectrodes apart, they would spring back. In addition, there is a dangerthat emissive material may reach the next-following electrode, with allthe disadvantages attendant thereon.

The said disadvantages are obviated to a great extent, if in an electricdischarge tube comprising an electrode system having a disc-shapedcathode of which the surface facing the nextfollowing electrode iscoated with emissive material, this surface has arranged on it a bareconductor, the diameter of which is larger than the thickness of theemissive layer but is smaller than the distance from this surface to thenextfollowing electrode. When correctly spacing apart the cathode, whichmust be displaceable towards the next-following electrode, the cathodeis first moved towards this electrode until the bare wire, which,according to the invention, extends across the upper surface of thecathode, just contacts with the said next-following electrode withoutthe cathode exerting any appreciable pressure on this electrode. Thecathode is then removed again from the said electrode with the use of amicrometer screw device until the desired spacing is reached and thentightly secured in position. These operations are ef- 1 dam. (c1.sue-mo) fected after all the glass sealsjof the tube are completed sothat, once the cathodeis adjusted, they can no longer aifect thisadjustment; It is advantageous to use a cathode as: described in U. S,application Serial No. 42,268 filed August 3, 1948, in which thedisc-shaped emissive part of the cathode is secured to a cylinderpreferably made of perforatedmetal, said cylinder' bein'g adapted tomove with some friction in'a metal tube sealed in the tube wall. Aftercorrect positioning, the metal cylinder is secured in the sealed-in tubeand soldered to it in a vacuumtight manner. Since the thickness of theemissive layer and that of the bare wire on the cathode surface embeddedin this layer are known, the correct spacing between the emissive layerand the next-following electrode may be adjusted with the use of themicrometer screw. This next-following electrode may be an anode, butalso a grid consisting of fine wires. Since the instant of engagement ofthe bare wire with this electrode is indicated by the passage of currentdue to the contact between wire and electrode, this instant may beascertained without the need of exerting any pressure on the saidelectrode and hence difficulties due to resilient deformations need notbe feared.

In order that the invention may be more clearly understood and readilycarried into efiect, it will now be described more fully with referenceto the accompanying drawing, in which Fig. 1 shows one arrangement ofcathode and anode of a diode system, i

Fig. 2 denotes the instant of contact between these electrodes and Fig.3 is a cross-sectional view of a discharge tube in accordance with theinvention.

Referring to Fig. 1, I designates the cathode proper, which is arrangedopposite an electrode 2, in this case the anode of a diode system, at adistance of, say, microns or less. The cathode l is secured to acylinder 3 and has its surface 4 coated with emissive material. Theemissive layer has a thickness of, say, 20 microns. Secured to the uppersurface is a bare wire 5 thirty microns in diameter, which thus extendsby 10 microns beyond the emissive layer. After the emissive layer hasbeen applied, the upper surface of the bare wire may, if necessary, befreed from emissive material by scratching. I'he cathode l is firstmoved towards the anode 2 till the bare wire '5 just contacts with thisanode, which may be ascertained by the establishment of an electriccontact, with the result that a circuit is closed through a measuringinstrument 6 and a battery I. With the use of a micrometer screw device(not shown), the cathode is then moved back by, say, 40 microns, so thata spacing of 50 microns between emissive layer and anode is obtained. Bythen soldering the cylinder 3 in positiomit is made sure that theadjusted spacing remains unaltered. In the case of even'smaller spacingsthe thermal expansion of cathode and anode will have to be allowed for.

The discharge tube shown in Fig.3 comprises a cathode I having a spacingconductor 5 arranged on the surface thereof and having a thicknessgreater than the thickness of the emissive layer 4. Positioned adjacentthe cathode with precision spacing is a grid 2 andpremote.

from the cathode is an anode iii. The respective elements are securedtogether byinsulating spacers ll, 8 and 9 which also form part of thetube envelope.

Although one embodiment has been described,

itis possible to use disc-shaped cathodes of dif- What I claim is:

An electron discharge tube comprising a, discshaped cathode, a secondelectrode in spaced relationship to said cathode, an emissive layer ofgiven thickness positioned on a portion of said cathode facing saidsecond electrode, and a bare conductor member positioned on a secondportion of said cathode surface free of emitting material and extendingdiametrically thereacross, said conductor and having a thickness greaterthan-said given thickness and less than the spacing between said cathodeand said second electrode. V

CAREL PETER KLbPPING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,17%,853- Bowie Oct 3-, 19392,225,465 Scharfnagel new- Dec. 17,1940 2,227,017, Schlesinger s- .aDec. 3t, 1940 2,411,184 Beggs -c-e- -Nov. 19, 1946 2,446,765 Hickey eta1 Aug. 1 0, 1948 2,458,693 Drieschman 'et al. Jan.- ll, 1949

